1. Field of the Invention
The present invention relates to a living body impedance measuring instrument, and a body composition measuring instrument for producing a body composition in a whole body or in a part of a body of a person to be tested, based upon the living body impedance measured.
2. Description of the Prior Art
It is well known to predict a body composition using a living body impedance (see, for example, xe2x80x9cAssessment of fat-free mass using bio-electrical impedance measurement of the human bodyxe2x80x9d, The American Journal of Clinical Nutrition, 41(4), 810-817, 1985). A number of body fat measuring instruments based on this principle have been proposed (see, for example, U.S. Pat. No. 4,008,721; Japanese Patent Publication No. 5-49050; and Japanese Utility Model Laid-Open No. 3-27050) and a number of xe2x80x9cBIMxe2x80x9d type body fat measuring instruments are now available in the market.
Those prior art instruments include two high frequency current application electrodes and two potential difference measurement electrodes required for measuring the living body impedance. One high frequency current application electrode is paired with one potential difference measurement electrode, and a high frequency current application terminal and a potential difference measurement terminal are disposed at the same end. Then they are attached to hands or feet of a human body. In order to produce a body composition, impedance values measured between a hand and a foot, between both feet or between both hands are basically utilized to derive a whole body composition. Therefore, in the past, the body composition is not necessarily produced by taking into account of a living impedance data in whole body.
If it is necessary to change the parts to be measured for getting more precision in measurement, it is frequently difficult to remove and re-attach the electrodes because of paired connection of the high frequency current application electrodes and the potential difference measuring electrodes. Sometime, it is even necessary to take off one""s clothes depending on the parts to be measured.
The prior art four-electrode measuring process can only measure the living body impedance between both feet or between both hands. Accordingly, it is difficult to measure the living body impedance a part by a part of the body.
Therefore, in case where the living body impedance should be measured a part by a part of the body, it is necessary for a skilled person to attach four or more electrodes to the relevant parts of the body. In addition, the voltage value measured should be converted into the data such as the impedance on the parts or the body compositions by using highly complicated calculation process. This involves highly expert knowledge and complicated arithmetic operations.
Another approach has been attempted using four pairs of electrodes each mounted for each of both hands and both feet. The electrodes are switched to perform measurement between different parts of the body. For example, the measurement may be performed between both hands, both feet, the right hand and the right foot, the right hand and the left foot, the left hand and the left foot or the left hand and the right foot (see Japanese Patent Laid-Open No. 9-285455).
However, such approach is defective in that the data required for calculating the values on the parts to be measured involves many unnecessary components so that the measuring process is highly complicated. In addition, even when it is desired to only measure the main body portion, it is very cumbersome to perform because of four different types of data and the different calculations based on such data required. Furthermore, because of possibility of relatively large error inherently generated in the measurement of living body impedance, an amount of error cumulatively increases in proportion to the number of different data types used. Therefore, such approach involves a higher risk especially when it is used to measure the lower impedance portions such as the main body portion.
In view of the above, there is a need to mitigate or to eliminate the disadvantages of the prior art devices as above. Therefore, one object of the present invention is to provides an improved measuring system that requires no cumbersome repeated attaching and detaching operations for the electrodes, that permits easy measurement of the impedance on each of different parts of a body, and that can produce precise values of body compositions based on the impedance data measured.
According to the present invention, high frequency current application electrodes are brought into contact with both hands, both feet, etc., which are extreme parts of a body in order to apply current to the parts of the body to be measured. Potential difference measurement electrodes are brought into contact with the parts to be measured along the path of the high frequency current. High frequency current application electrodes and potential difference measurement electrodes are selected to select the path of the high frequency current and the path of the potential difference measurement in accordance with the purpose.
Potential difference is allowed to be appeared only on the parts of a body that are included in the path of high frequency current according to 4-terminal law, and therefore, potential difference in any of sections along the path of high frequency current can be measured. As the result, the path of high frequency current and the potential difference measuring sections along the path can be selected in any combination to measure the impedance on desired parts of the body.